1. Field of the Invention
The present invention relates to a flexible printed circuit performing signal transmission from one device to another device, and a touch panel, a display panel and a display each of which includes the flexible printed circuit.
2. Description of the Related Art
Techniques of detecting a position touched by an object to be detected such as a finger or a pen on a display surface of a display have been heretofore known. Among them, a typical and widespread technique is a display including a touch panel. There are various types of touch panels, but a resistive touch panel is commonly used. In the resistive touch panel, a panel surface has a laminate configuration in which a very small spacer is sandwiched between glass and a film opposed to each other, and a transparent electrode grids are arranged on opposed surfaces of the glass and the film. Then, when a finger or a pen touches a surface of the film, the film is bent, and a transparent electrode on the surface of the film and a transparent electrode on the surface of the glass are brought into contact with each other, so that a current flows. Thereby, the position of the finger or the pen is detected by measuring a partial pressure ratio between the resistance of the transparent electrode on the surface of the glass and the resistance of the transparent electrode on the surface of the film. Therefore, when such a touch panel is used, users intuitively operate the touch panel.
FIG. 62 illustrates an example of a sectional configuration of the above-described resistive touch panel. A touch panel 100 illustrated in FIG. 62 includes a pair of transparent substrates 200 and 300 which are opposed to each other with a predetermined space in between, resistive films (not illustrated) arranged on opposed surfaces of the pair of transparent substrates 200 and 300, connection terminals 210 and 310 electrically connected to the resistive films, respectively, a flexible printed circuit (FPC) 400 electrically connected to the connection terminals 210 and 310, and an adhesive layer (not illustrated) bonding the transparent substrates 200 and 400 together with the FPC 400 in between.
Four connection terminals 210 are arranged on a surface where the resistive film is arranged of the transparent substrate 200 at regular intervals, and are bonded and connected to an anisotropic conductive film 410 (which will be described later) arranged on one surface of the FPC 400. Moreover, two (in FIG. 62, the second and the fourth connection terminals 210 from the left) of the four connection terminals 210 are connected to an end of the resistive film on the transparent substrate 200, and the other two (in FIG. 62, the first and the third connection terminals 210 from the left) of the four connection terminals 210 are so-called dummy terminals, and they are arranged so as to keep a constant space between the transparent substrate 200 and the anisotropic conductive film 410 of the FPC 400.
Four connection terminals 310 are arranged on a surface where the resistive film is arranged of the transparent substrate 300 at regular intervals, and are bonded and connected to the anisotropic conductive film 410 arranged on the other surface of the FPC 400. Moreover, two (in FIG. 62, the second and the fourth connection terminals 310 from the left) of the four connection terminals 310 are connected to an end of the resistive film on the transparent substrate 300, and the other two (in FIG. 62, the first and the third connection terminals 310 from the left) of the four connection terminals 310 are so-called dummy terminals, and they are arranged so as to keep a constant space between the transparent substrate 300 and the anisotropic conductive film 410 of the FPC 400.
As illustrated in FIGS. 63 to 66, the FPC 400 has a strip shape extending in one direction. FIG. 63 illustrates a schematic configuration of one surface of an end of the FPC 400, and FIG. 64 illustrates a schematic configuration of the other side of FIG. 63. FIGS. 65 and 66 illustrate sectional views taken along lines A-A and B-B, respectively, in the direction of arrows in FIG. 63. An end of the FPC 400 is sandwiched between the pair of transparent substrates 200 and 300, and the other end of the FPC 400 is connected to a device (not illustrated) processing an output signal from the touch panel 100. The FPC 400 includes a flexible base film 420 extending in a direction where the FPC 400 extends. An end section of the base film 420 is sandwiched between the pair of transparent substrates 200 and 300.
Four pairs of wiring layers 430 and 440 are arranged so as to be opposed to each other with the end section (hereinafter referred to as transparent substrate-side end section) sandwiched between the pair of transparent substrates 200 and 300 of the base film 420 in between. The wiring layers 430 on a side close to the transparent substrate 200 are transparent substrate-side end section, and four wiring layers 430 are formed in an island shape in regions opposed to the connection terminals 210. On the other hand, four wiring layers 440 on a side close to the transparent substrate 300 are formed linearly from regions opposed to the connection terminals 310 to an end section opposite to the transparent substrate-side end section of the base film 420.
Plating layers 450 are arranged at least on surfaces on a side close to the transparent substrate-side end section of the wiring layers 430 and 440. Two through holes 460 penetrating through the base film 420 are arranged in the transparent substrate-side end section of the base film 420. The two through holes 460 penetrate through two pairs (in FIG. 62, the second and the fourth pairs from the left) of wiring layers 430 and 440, respectively, from among the four pairs of wiring layers 430 and 440, and the plating layers 450 arranged in contact with the wiring layers 430 and 440 through which the through holes 460 penetrate are integrally formed. Thereby, the wiring layers 430 and 440 in each of the two pairs (in FIG. 62, the second and the fourth pairs from the left) from among the four pairs of wiring layers 430 and 440 are electrically connected to each other via the through holes 460.
In addition, the wiring layers 430 and 440 in each of the other two pairs (in FIG. 62, the first and the third pairs from the left) through which the through holes 460 do not penetrate from among the four pairs of wiring layers 430 and 440 are electrically separated from each other. Therefore, the wiring layers 430 through which the through hole 460 do not penetrate (in FIG. 62, the first and the third wiring layers 430) from among the four wiring layers 430 are so-called dummy wiring layers, and are arranged so as to keep a constant space between the base film 420 and the anisotropic conductive film 410.
Plating layers 470 are further arranged on surfaces of the plating layers 450. The plating layers 470 on a side close to the transparent substrate 200 are coupled to the anisotropic conductive film 410 formed on a surface of the transparent substrate 200, and the plating layers 470 on a side close to the transparent substrate 300 are coupled to the anisotropic conductive film 410 formed on a surface of the transparent substrate 300. Therefore, in the touch panel 100, two connection terminals 210 (in FIG. 62, the second and the fourth connection terminals 210 from the left) coupled to the resistive film on a side close to the transparent substrate 200 are electrically connected to two wiring layers 440 (in FIG. 62, the second and the fourth wiring layers 440 from the left) via the through holes 460, and two connection terminals 310 (in FIG. 62, the first and the third connection terminals 310 from the left) coupled to the resistive film on a side close to the transparent substrate 300 are electrically connected to two wiring layers 440 (in FIG. 62, the first and the third wiring layer 440 from the left) not via the through holes 460 but via the plating layers 450 and 470.
Moreover, as illustrated in FIGS. 62 to 63, in the FPC 400, a coverlay 490 which protects the wiring layers 440 and the plating layers 450 from outside is bonded to a surface on a side close to the wiring layer 440 of the FPC 400 by an adhesive layer 480.
A typical configuration of the resistive touch panel is described in, for example, Japanese Unexamined Patent Application Publication No. 2002-182854 or the like.